To cope with the problems caused by air pollution and global warming, reducing the carbon dioxide emission is desperately needed in recent days. The automobile industry focuses on introduction of an electric vehicle (EV) or a hybrid electric vehicle (HEV) to reduce the carbon dioxide emission. In this connection, an electrical device like a secondary battery for driving a motor, which is a key element for commercialization of such vehicles, is actively developed.
As the secondary battery for driving a motor, a lithium ion secondary battery having a high theoretical energy has been getting an attention and has been actively developed in these days. The lithium ion secondary battery generally has a constitution where a positive electrode formed by applying a slurry for a positive electrode containing a positive electrode active material to the surface of a collector, a negative electrode formed by applying a slurry for a negative electrode containing a negative electrode active material to the surface of the collector, and an electrolyte disposed between the positive and negative electrodes are housed in a battery casing.
For the improvements of capacity characteristics and output characteristics of the lithium ion secondary battery, the choice of each active material is critically important.
Conventionally, there has been proposed a cathode composition for a lithium ion battery, represented by a formula (a) Liy[M1(1-b)Mnb]O2 or (b) Lix[M1(1-b)Mnb]O1.5+c (In the formula, 0≦y<1, 0<b<1 and 0<c<0.5 and M1 represents one or more kinds of metal elements; however, in the case of (a), M1 represents a metal element other than chromium), the composition being in a form of a single phase having an O3 crystal structure that does not undergo a phase transformation to a spinel crystal structure when incorporated in a lithium ion battery and cycled for 100 full charge-discharge cycles at 30° C. and a final capacity of 130 mAh/g using a discharge current of 30 mA/g (see Patent Document 1).
However, the present inventors studied it and found it bearing a problem that, even in a lithium ion battery using the cathode composition for a lithium ion battery discussed in Patent Document 1, the discharge capacity, the discharge operating voltage and the initial rate characteristic are not enough.
The present invention is provided in view of the problems that the conventional technique has, the object of which is to provide a positive electrode active material, a positive electrode for an electric device, and an electric device, all of which make it possible to achieve excellent discharge operating voltage and initial rate characteristic while maintaining a high discharge capacity.